This guide is derived and condensed from Danziger's Hypericum Cultivation Description. We highly recommend reading it in its entirety, as it contains essential growing information. Danziger is the breeder of our GypsophilaVeronica SkylerGlory Solidago, and Scoop Scabiosa

Common Name Hypericum (aka St. John's Wort)         
Genus  Hypericum
Species various 
Family Clusiaceae / Guttiferae 
Life Cycle  Can be annual or perennial, shrub or deciduous tree.
Tray Size  50 (Half Tray)
Plug Care
Harden off for the field, or transplant right away into a tunnel. If you cannot transplant, bump up to larger pots. During the first ten days after transplant (establishment stage), overhead irrigation should be used and can be supplemented with drip irrigation and fertilizer. 
Netting / Staking Support netting is recommended. 30% shade cloth can be used in summer to protect berries and foliage from discoloration. This may not be necessary.
Temperature Range Ideal temperature range is 75-80F daytime. 55-60F night. They are adaptable outside of this range.
Spacing 9"
Soil Preference Adaptable to various moist well drained soils
Day Length Short days put on vegetative growth; long days initiate flowering. 
Pinching Pinching to a minimum of 7-10 internodes
from the plant’s base (at least a month after planting), allowing growth of side stems. 
When to Plant Late spring or early fall during short days
Harvesting Harvest is carried out when about 80% of the berries on the branch are ripe and colored, and almost all of the flowers have dropped. Cut back to just a couple of inches, to allow them to regrow.
Post Harvest Care Harvest in the early morning before conditions become too hot.  Harvest directly into water with solution.  Remove all foliage from lower 1/3 of branch. 
Diseases / Insects Rust can be an issue in very humid conditions. Nematode gall in roots. 
Bailey's Notes Hypericum seems to be hardier and more adaptable than I would have imagined. I have reports of success from Philadelphia to Indiana to Oregon. When it is established you can expect 2 to 3 harvests per season. Just prune it back hard after each harvest and allow to regrow. 

Danziger Hypericum Agricultural Info (scroll down to lower left side of page)

Danziger Hypericum Culture Description